Hexafluorophosphates as first stage additives



United States Patent ()ffice Patented Feb. 4, 1969 3,425,996HEXAFLUOROPHOSPHATES AS FIRST STAGE ADDITIVES Mary E. Carter,Philadelphia, and John A. Price, Swarthmore, Pa., assignors to FMCCorporation, Philadelphia,

Pa., a corporation of Delaware No Drawing. Filed Oct. 3, 1966, Ser. No.583,950 U.S. Cl. 26075 7 Claims Int. Cl. 'C08g 17/08 ABSTRACT OF THEDISCLOSURE Process of preparing polyethylene terephthalate whereinterephthalic acid and ethylene glycol are esterified in the presence ofa hexafluorophosphate esterification additive selected from the grouphaving the formulas MOPF and NH PF -NH F, wherein M represents a metalfrom Groups I-A or VII of the Periodic Table or an NH -group or loweralkyl substituted NH -group to form a polyester prepolymer and then saidprepolymer is polycondensed in the presence of a polycondensationcatalyst.

This invention relates to a method of preparing filarnent-forming linearpolyesters. In particular, it relates to a method of preparingpolyethylene terephthalate resin having excellent filament-formingproperties.

The manufacture of filament-forming polyester resin from a dicarboxylicacid and a diol is well-known in the art. Generally, in the preparationof such polyesters, a dicarboxylic acid and glycol are first combinedand subjected to a direct esterification reaction. The resulting productor prepolymer is then polycondensed at higher temperatures and underreduced pressure in the presence of a polycondensation catalyst to formthe desired filament-forming polyester resin. Various additives havebeen suggested heretofore for use in the first stage or esterificationstep to enhance the reaction. However, generally, none of these haveproved entirely satisfactory since many of those known, for instance,are not capable of producing suitable prepolymers for preparing linearpolyester resins having sufliciently high molecular weights within arelatively short reaction period. From a commercial standpont, it isessential that a polyester resin be produced in the shortest possibletime and that the desired degree of polymerization be obtained. Apolyethylene terephthalate resin suitable for melt spinning intofilaments should have a carboxyl content value of about below 50equivalents per million grams (eq./ gr. or meq./kg.), an intrinsicviscosity preferably not less than about 0.60 and a birefringent meltingpoint of at least about 25 8-260 C. Additionally, it is essential thatsuch filaments be substantially colorless, possess a high degree oftenacity and hydrolytic and thermal stability.

It is an object of this invention to prepare polyethylene terephthalateresin suitable for melt extrusion into nondegraded processable filamentsby a direct esterification and polycondensation procedure.

Another object of the present invention is to provide an improved methodfor completing the direct esterification reaction between ethyleneglycol and terephthalic acid in the preparation of polyethyleneterephthalate.

These and other objects are accomplished in accordance with the presentinvention which involves a method of preparing filament-formingpolyethylene terephthalate wherein the terephthalic acid and ethyleneglycol are directly esterified and the product of esterification ispolycondensed in the presence of a condensation catalyst, theimprovement comprising carrying out the direct esterification reactionin the presence of an additive compound, containing phosphorous in itshighest oxdative state (+5) in the form of a fiuoro complex anion,selected from the group having the formulas M(PF and NH,PF -NH F,wherein M represents a metal from Groups I-A and VIII of the PeriodicTable (see Merck Index, sixth edition, inside front cover) or anNH-group or substituted NH,- group where at least one hydrogen atom hasbeen substituted with a lower alkyl radical containing from about 1 to 6carbon atoms, x is l Where M is a monovalent metal or an NH -group orsubstituted NH -group and x is 2 where M is a divalent metal, in anamount sufiicient to improve the properties of the resulting polyester.

The hexafluorophosphate compounds that are used in the directesterification step of the present invention may be suitably varied tomeet any requirements of reaction conditions and desired product. Forexample, among the first stage or esterification additives that can beused in accordance with the present method are cesiumhexafluorophosphate, tetramethylammonium hexafluorophosphate, potassiumhexafiuorophosphate, nickel hexafluorophosphate, and ammoniumhexafluorophosphate fluoride.

Generally, a catalytic quantity of the present hexafluorophosphatecompounds in the range of from about 5 10 to and 5 X 10* mole per moleof terephthalic acid in the subject terephthalic acid-ethylene glycolreaction mixture is used in the present direct esterification method.Higher or lower concentrations of the present catalysts can also beused. However, when concentrations less than the above are used.However, when concentrations less than the above are used, theireffectiveness is generally reduced whereas if concentrations greaterthan this are used, no further improvement in the present method ordesired product is generally obtained.

In general, the preparation of filament-forming polyesters of thepresent invention via the direct esterification reaction is carried outwith a molra ratio of ethylene glycol to terephthalic acid from about1:1 to about 15:1 but preferably from about 1.2: 1 to about 2.5: 1. Thefirst stage direct esterification step of the present method isgenerally carried out at temperatures ranging from about 220 C. to about290 C. in the absence of an oxygen containing gas at atmospheric orelevated pressure for about three to five hours. For example, thereaction may be carried out in an atmosphere of nitrogen. The secondstage or polycondensation step of the present method is generallycarried out under reduced pressure within the range of from about 0.05to 20 mm. of mercury in the absence of an oxygen containing gas attemperatures from about 260 to 325 C., for about two to six hours.

When the direct esterification step is completed, as indicated, forexample, by collection of a clear distillate, any remaining glycol isdistilled oh and a polycondensation catalyst is added to the esterifiedreaction product.

The polycondensation step of the present method is accomplished throughthe use of a conventional condensation catalyst for example, antimonytrioxide, antimony pentoxide, antimony trisulfide, antimony trifiuoride,antimony triphenyl, zinc acetylacetonate, and the like. Thepolycondensation catalyst may be added. to the present reaction mixturebefore initiating the first stage or direct esterification reactionbetween ethylene glycol and terephthalic acid or after the reactionproduct thereof is formed. The polycondensation catalysts are generallyemployed in concentrations ranging from about 0.005 to about 0.5%, basedon the total weight of the reactants.

The process of this invention may be carried out either continuously orbatch-wise.

The following examples of several preferred embodiments will furtherserve to illustrate the present invention. All parts are by weightunless otherwise indicated.

3 4 EXAMPLES We claim: 1. In a method for preparing filament-formingpolymlxlure contamm'g 84 grams mole) of t ethylene terephthalate whereinterephthalic acid and thalic acid, 62 grams (1.0 mole) of ethyleneglycol, a d ethylene glycol are directly esterified and the product ofmole of E hexafluoroPhosphate compPund as esterification ispolycondensed in the presence of a conlfsted in the follovflng f Wlththe exact Welgh? used 0 densation catalyst, the improvement comprisingcarrying the above reaction mlxtur?! was h to a Escher" out the directesterification reaction in the presence of a Porter pmssulfg as semblyequlPPed Wlth a nltrogen sparge catalytic quantity of an etserificationadditive, containing tube and a distilling arm. The reactor was loweredinto phosphorous in its highest oxidative state (+5) in the an 011 hmamtanled at 2600 and flushed for ten 10 form of a fluoro complex anion,selected from the group minutes With dry nltrogen. A n1trogen pressureOf 60 having the formulas M(PFG)X and NHiPFKNHiFWhCffi p.s.i. wasapplied and a distillate of water-ethylene glycol in M represents ametal from Group VII of the was collected. When a clear liquid, i.e.solution, was ob- Periodic Table or an NH4 grOup or substituted NH4group tained, the pressure was reduced to atmospheric and the Where atleast one hydrogen atom has been Substituted remaining excess glycol wasdistilled. The resulting low with a lower alkyl radical containing fromabout 1 to 6 molecular weight prepolymer was further reacted undercarbon atoms, x is 1 Where M is a monovalent metal or a nitrogen blanketin the presence of 0.04%, based on an NH4 group or Substituted NHygmupand x is 2 Where the weight of the prepolymer, of a conventional poly- Mis a divalent metal condensation catalyst, e.g. antimony trioxide, undersub- The mfithod of claim 1 wherein the additive atmospheric pressure ofabout 0.1 mm. of mercury for pound is Present in an amount ranging fabout four hours at 282 C. to a high molecular weight poly- 5 1 s toabout -2 mole per mole f terephthailic ester. acid.

The following table sets forth conditions and results of 3. The methodof claim 1 wherein the additive is tetravarious reactions carried out asdescribed above. methylammonium hexafluorophosphate.

TABLE Weight of hexa- Esterifica, Prepolymer Condensa- Polymer car- Ex.Ester-ification additive fiuorophosphate tion time, carboxyl contionIntrinsic boxyl con- Melting N0. compound used, hrs.:mins. tent,meq./pg. catalyst viscosity tent, meqJkg. point, 0.

1 None 3:40 316 0.36 2 Tetramethylammonium hexa- 0.0110 3:30 113 SbzOs1.0 261 fiuorophosphate. 3 Cesium hexafiuorophosphate 0.0139 3:05 184Sb203 0. 78 18 2 4 Nickel hexafluorophosphate 0.0174 5:00 18.0 SbzOs1.00 27 258 5 Potassium hexaflu0roph0sphate 0.0092 3:55 137 813203 0.9039 258 6 Ammonium hexafluorophosphatc 0.0100 3:00 145 SbzOa 2 0.72 29260 fluoride.

l 2% hours polycondensation time. 5 2 hours 45 minutes polycondensationtime.

The results shown in the above table indicate that the 4. The method ofclaim 1 wherein the additive is cesium presence of a hexafluorophosphatecompound during the hexafluorophosphate. direct esterification step inthe production of filament- 40 5. The method of claim 1 wherein theadditive is nickel forming polyester resin, in general, facilitates theprepahexafluorophosphate. ration of and improves the prepolymer formedand in 6. The method of claim 1 wherein the additive is potasturn thepolyester resin product. Through the use of such m h xaflllorophosphate.an additive, the direct esterification reaction time is re- The methodof claim wherein E116 additive s amduced and the resulting prepolymeris, in general, charmQnium hexafluorophosphatfi fluorideacterized asbeing a more highly esterified product than one produced when noesterification additive is used, as indicated by the carboxyl content ofthe prepolymers. UNITED STATES PATENTS Further, the prepolymers of thepresent method can be 3,048,564 8/1962 Helfelfinger. condensed to yieldpolyester resins which have a high molecular weight, as indicated bytheir high intrinsic vis- WILLIAM SHORT, P rim!" 3 Examine"- ReferencesCited cosity and melting Point L. P. QUAST, Assistant Examiner.

Various changes and modifications may be made practicing the inventionWithout departing from the spirit and US. Cl. X.R.

scope thereof, and therefore, the invention is not to be 260-475 limitedexcept as defined in the appended claims.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,425,996 February 4, 1969 Mary E. Carter et al.

It is certified that error appears in the above identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 1, line 20, "VII" should read VIII Column 2, line 2, "oxdative"should read oxidative line 7, after "NH" first occurrence, insert 4 line25 "and should read about lines 29 and 30, cancel "However, whenconcentrations less than the above are used, line 3'7, "molra" shouldread molar Column 4, line 8, "ecserification should read esterificationline 12, "Group" should read Groups same line 12, "VII" should read VIIIline 13, after "Table" insert M (Merck Index, Sixth Edition) Columns 3and 4, in the heading to the table, fifth column, line 3 thereof, "pg.should read kg.

Signed and sealed this 24th day of March 1970.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, a Attesting OfficerCommissioner of Patent

